1. Field of the Invention
The present invention relates generally to an apparatus and a method for calibration in a multi-antenna system. More particularly, the present invention relates to an apparatus and a method for carrying out calibration without separate transmission and reception paths for the calibration in the multi-antenna system.
2. Description of the Related Art
A multi-antenna system may minimize interference by forming a beam toward a receiving end to transmit a signal using smart antennas or a beamforming device. For the beamforming, the multi-antenna system applies a beam coefficient per antenna. Using an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, the multi-antenna system applies the beam coefficient per tone with respect to the respective antennas.
To apply the beam coefficient per antenna, a transmitting end of the multi-antenna system needs to control phase and magnitude of signals input to the antennas. The transmitting end conducts calibration to avoid distortion of the phase and the magnitude of the signals according to nonlinear characteristics of elements constituting a transmission path and a reception path.
FIG. 1 depicts a conventional calibration apparatus in a multi-antenna system.
In the multi-antenna system of FIG. 1, a transmitting end includes NT-ary antennas, couplers 100-1 through 100-NT, Time Division Duplex (TDD) switches 110-1 through 110-NT, transmitters 120-1 through 120-NT, receivers 130-1 through 130-NT, Digital Up Converters (DUCs) 140-1 through 140-NT, Digital Down Converters (DDCs) 150-1 through 150-NT, a controller 160, a compensation signal processor 170 and a compensation transceiver 180. Herein, transmission paths and reception paths of the antennas operate substantially the same. Thus, the transmission path and the reception path for the first antenna are illustrated by way of example.
In the calibration of the transmission path, the controller 160 forwards a compensation signal output from the compensation signal processor 170 to the DUC 140-1.
The DUC 140-1 oversamples the compensation signal fed from the controller 160.
The transmitter 120-1 converts the signal output from the DUC 140-1 to a Radio Frequency (RF) signal.
The TDD switch 110-1 transmits the RF signal output from the transmitter 120-1 to the coupler 100-1. That is, the TDD switch 110-1 switches to connect the transmitter 120-1 and the coupler 100-1 in the transmission interval.
The coupler 100-1 transmits the RF signal provided from the TDD switch 110-1 via the antenna. The coupler 100-1 couples the RF signal to the compensation transceiver 180.
The compensation transceiver 180 converts the RF signal fed from the coupler 100-1 to a baseband signal and outputs the baseband signal to the compensation signal processor 170. The compensation transceiver 180 includes a divider 181, a TDD switch 183, a transmitter 185, a receiver 187, a DUC 188 and a DDC 189. Herein, the components of the compensation transceiver 180 operate the same as the components of the transmission path and the reception path of the antennas and shall not be described.
The compensation signal processor 170 examines the distortion of the transmission paths connected to the respective antennas using the signals provided from the compensation transceiver 180 and calibrates the transmission path.
The transmitting end generates the beam coefficient for the beamforming by taking into account the distortion of the transmission paths confirmed at the compensation signal processor 170.
In the calibration of the reception path, the compensation signal processor 170 transmits the compensation signal to the compensation transceiver 180 under the control of the controller 160.
The compensation transceiver 180 converts the baseband compensation signal fed from the compensation signal processor 170 to an RF signal and outputs the RF signal to the coupler 100-1 of the antenna via the divider 171.
The coupler 100-1 combines the RF signal fed from the compensation transceiver 180 with the signal received via the antenna and transfers the combined signal to the receiver 130-1 via the TDD switch 110-1.
In the reception interval, the TDD switch 110-1 switches to connect the receiver 130-1 and the coupler 100-1.
The receiver 130-1 converts the RF signal output from the TDD switch 110-1 to a baseband signal and transmits the baseband signal to the controller 160 through the DDC 150-1.
The controller 160 detects the compensation signal from the signal output from the DDC 150-1 and outputs the detected compensation signal to the compensation signal processor 170.
The compensation signal processor 170 examines the distortion of the reception paths connected to the respective antennas using the compensation signals provided from the controller 160 and calibrates the reception paths.
As discussed above, to compensate for the magnitude and the phase of the signals of the transmission path and the reception path by means of the calibration, the multi-antenna system requires separate transmission and reception paths. Accordingly, the transmitting end and the receiving end of the multi-antenna system are subject to the increased complexity and the raised cost due to the separate compensation transceiver for the calibration.
Therefore, a need exists for a system and method for calibrating transmission paths and reception paths in a multi-antenna system by reducing costs and increasing the calibration accuracy.